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Will a 2-bolt FE block handle 6500?
Do I need a girdle?
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The 2 bolt FE blocks will handle 6500rpms depending on the stroke and HP you make. They seem to be able to handle 600HP and then you need a girdle. Thanks, Keith
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Yes,
It isn't the rotational velocity you need to worry about. You can spin a well balanced engine to 8,000 rpm and it will live through millions of cycles (rpms). Are you asking whether an FE street car can turn 6500? sure it can provided you give it the tools it needs, solid lifters valve train... The 4 bolt 406's came about when ford tried turning 8.000 rpm in a 5200 pound car for 500 miles. It's the loading and unloading of the crank saddles you need to worry about. Obviously the loading and unloading of a 400-450 hp engine is far less, 25- 30% less than a 600 hp FE. A 2500 pound street car driven responsibly can occasionally turn 6500 for years and years... But why risk it??? A good seasoned FE block is $1,000. a new genesis block is $4,000... Is the $3,000 you save really going to break you? |
Rotational velocity I'm not worried about. From an engineer's point of view, it's a fatigue cycle. A piston trying to drive the crank through the bottom of the engine 4000 times a minute is less harsh than one trying to drive the crank through the bottom 6500 times a minute.....you had it with the loading/unloading you were describing. Two bolts/studs sunk through a bearing saddle and a main cap is all that's keeping it from coming out. What's the fatigue stress of an ARP main stud? What's its natural frequency?
Usually at those rpm's you're at wide open throttle also....so you're not cutting it any slack. Regarding everything else, I was worried about a 2-bolt main block taking lots and lots of stress. And yes, the extra $3k would break me. Considering the car is about 70% finished, I just finished building a 425ci SBF, and now I'm starting another engine build. I can't afford the extra $3k for a shiny new block like some other people can. Thanks for the input guys.... Onto the next step. |
Brent,
Is this going to be a race only motor? If not, probably 95% to 98% of the time it's going to be in a much lower RPM range. I have turned stock 390 short block(cam and heads of course) 6200 to 6300 many times years ago and never hurt the lower end. The lower end was and is an FE's strong point. Build what you want and don't worry about the occasinal blast to 6500. Just be sure and use good valve train with hardend rocker shafts. Enjoy, Byron W. |
Not a race motor. Just a street/strip deal.
Working on a head/cam/stroke package with a peak rpm between 6000-6500. I figure if it peaks at 6200, then I'd have to shift it at 6400-6500. I'll definitely look into the quality rocker shafts and valve train components... |
The problem with the 2-bolt block is not the fact that it is 2 bolt but the way ford designed the main webbing. The blocks have the oil hole from the camshaft to the mains right down the middle of the block. This is weak erea of the block. The weight of the rotating assembley and the rpms are the most important thing hear. The blocks try to split and do split down the number 2 and 4 mains which causes loss of oil pressure and bearing loss. You should have no problems with what you are doing. Like I said before we have seen these blocks split at 550 to 600 HP with rpm range in the 7000 range, these have been drag engines that do nothing but turn this rpm time and time again. Use the 2 bolts block with main studs and balance everyhting good and you will have no problems. Keith
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Thanks Keith.
Now I'm kinda taking a step back with head choices. I had initially planned on using some iron heads...but after sticking some flow numbers that I've found for various heads (C8AE-H, 427LR, 428CJ), most of them just don't seem up to par with the Edelbrock pieces. After finding out what it would cost to port a set of iron heads to flow reasonably well, plus surface the decks, mag them, etc....I think it would be worth my while to invest in the aluminum heads...then I could run another 1/2 point in compression and not worry about machining costs. I've seen LR and CJ heads in the $500-$600 range...but who knows how they've been treated....and they'd still have to be gone through. |
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